139 



Species a. (PI. XXIV, Fig. 3; PI. XXV, Fig. 1). The posterolateral 

 arms are fairly upright; they are about four times the body length, con- 

 siderably longer than the three inner pairs of arms, which are scarcely 

 twice the body length. The preoral ciUated band is straight, bending 

 abruptly downwards at the sides. The frontal area is distinct. 



Fig. 66. Skeleton of Ophiopluteus undulatus. ^'»/i. A. species a; 

 B. species a, var. (off Pulo Pisang); C. species b. Letters as in fig. 61. 



Fig. 67. Part of 

 posterolateral rod 

 of Ophiopluteus un- 

 dulatus. '»%. 

 A. B. from typical 

 form of species a; 

 C. from an abnorm- 

 al?) specimen. 



The skeleton (Fig. 66, A; Fig. 67, A, B). The body 

 rods are rather strongly curved, the end rods very short, 

 rounded, with three or four short prominences. The 

 transverse rods are short and thick, forming together 

 a small arch; the ends of the transverse rods abut on one another quite 

 simply, without any sort of widening or indentations. The undulations of 

 the posterolateral rods begin at about the level of the postoral ciliated 

 band and continue unto the point; in the outer part the undulations are 

 somewhat longer. A few short, straight thorns are found on the top of 

 each undulation on the adoral side, sometimes also on the outer side. 



18* 



